Prevent that a prefix flag is set based on invalid configuration data.The validity.verify_base flag should only be set for alias devices.Usually the unit address type is either one of base, PAV alias orHyperPAV alias. But in cases where the unit address type is not set orany other value the validity.verify_base flag might be set as well.This would lead to follow on errors.Explicitly check for alias devices and set the validity flag only forthem.